The present invention relates to a reverse combustion type combustion apparatus, and more particularly relates to such a combustion apparatus that is provided with an improved construction for an exhaust box.
From the past, heating devices with hot water supply function that are capable of operating by changing over between room heating operation and hot water supply operation have been widely employed. This type of heating device with hot water supply function typically comprises a combustion means, a heat exchanger for supplying heat to a room heating thermal medium, a circulation passage that connects the heat exchanger and a room heating radiator unit, a circulation pump provided in the circulation passage, a bypass passage that bypasses the room heating radiator unit, a heat exchanger partway along the bypass passage for supplying heat to cold water, and so on. In the case of relatively small combustion apparatuses of various types, including a heating device with hot water supply function of this type, in some cases, a reverse combustion type combustion system is adopted, in which the fuel is combusted in a downward direction.
The hot water supply apparatus disclosed in Japanese Patent Publication No. 3,435,976 is built as a reverse combustion type combustion apparatus in which a burner is disposed below a fan, a heat exchanger is disposed below the burner, an exhaust box is disposed below the heat exchanger, and a muffler (i.e. an exhaust duct) that is connected to the exhaust box is disposed at the rear side of the fan, the burner, and the heat exchanger, so that combustion takes place downward from the burner.
In a per se conventional reverse combustion type combustion apparatus, an exhaust box made from metal has been employed, but nowadays, in many cases, an exhaust box made from a synthetic resin material is being employed, and, since condensed water generated in the heat exchanger from the combustion exhaust gases drips down into the exhaust box, in order to enhance the performance for drainage of this condensed water, the bottom portion of the exhaust box is formed, not in a flat shape, but in a concave shape composed of a plurality of inclined surfaces, with a discharge port being formed at its lowermost portion.
On the other hand, when a combustion apparatus is being assembled on an assembly line, normally, an assembled equipment unit is manufactured in which a burner, a primary heat exchanger, a secondary heat exchanger, an exhaust box, and an exhaust duct are assembled together in the form of a unit, and this assembled equipment unit is then fitted into an outer casing together with other accessory equipment.
When employing an exhaust box made from metal, which has excellent strength, as in the case of the reverse combustion type combustion apparatus of above described Japanese Patent, it is common to form the bottom surface of the exhaust box as flat, so that, when the combustion apparatus is to be assembled on the assembly line, an assembled equipment unit can first be manufactured by attaching the heat exchangers and the burner to the exhaust box in the state in which the exhaust box is stood up by itself, and subsequently this assembled equipment unit is fitted into the outer casing.
However, since an exhaust box that is made from a synthetic resin material can be manufactured in any desired shape, accordingly in many cases, as mentioned above, in order to enhance the performance for drainage of condensed water, the bottom portion of the exhaust box is formed, not in a flat shape, but in a concave shape that includes a plurality of inclined surfaces. In such a case, it is not possible to assemble the heat exchangers and the burner to the exhaust box in the state in which the exhaust box is standing up by itself.
As an alternative, it would also be possible to assemble the burner, the heat exchangers, and the exhaust box in a state in which they are laid down on their sides, but in this case there is a danger that a part of one of the heat exchangers, or the passage portion of the exhaust duct, or a flange of a pipe connection portion or the like may be damaged; and this is also disadvantageous because the area which the assembled equipment unit occupies on the assembly line becomes larger.
As another alternative, it would be possible to adopt a method of assembly in which a temporary stand made from wood or synthetic resin is prepared, the exhaust box is fixed on this temporary stand in a vertical attitude, and then the heat exchangers and the burner are assembled to the exhaust box. However, this method of assembly is disadvantageous because it involves an additional manufacturing cost for the temporary stand and also a handling cost, and moreover it takes substantial time and effort to fix the exhaust box to the temporary stand and later to remove the completed assembly therefrom.
An object of the present invention is to provide a reverse combustion type combustion apparatus employing an exhaust box that is formed from synthetic resin, and that has a construction which makes it stand up by itself.